So how much liquid do we really need each day? Probably the most common answer I hear in my office from my patients and their families is the 8 and 8 answer. I’ve heard it so often that I’ve actually given it a name. The “8 and 8” means eight glasses of water eight times a day. That’s one gallon of water per day. Yikes!

I can tell you if I drank that much water each day, I wouldn’t be doing a lot of heart surgery.

If you’re inside a building that’s at the usual 72oF, you’ll lose about a quart and a half of water each day from the water vapor in your breath and evaporation from your skin. The rest of the water goes into the toilet from the usual two pathways. Obviously if you are exercising and working up a sweat, have a fever or just a bad case of diarrhea (is there a good case?) your fluid losses will go up. Under normal circumstances you need to consume about 2 quarts of fluid per day. The food you eat will typically give you the better part of a quart of water. And that’s it.

If you followed the “8 and 8” folklore you’ll be overshooting your average daily fluid requirements by a solid 50%. So what is with this current obsession of staying well-hydrated? Why have we become a nation of water-bottle toters? What led my fellow Potato River Falls explorers to bring various refreshments with them for what is no more than a thirty to forty minute trek up and down a mildly rugged hill to see something cool that Mother Nature put together for us?

In a word: Marketing.

In case you hadn’t heard, the profit margins on bottled water are astronomical. The bottle and its label cost more than what’s inside. The people that sell it want the people that buy it to buy as much as possible. That way they make the most money. That’s it. No magic. No mystery. Just a good, old-fashioned profit motive. And, no, these folks don’t care how many times a day you have to pee. In fact, I’d be willing to bet that the amount of water that’s wasted in all the extra flushing that our overly hydrated fellow citizens do is greater than the amount of water they drink – by a lot.

Now if you’re exercising or spend a lot of time in a warm environment your fluid needs can go way up. You can sweat out a quart or more in addition to the usual daily losses from evaporation. These losses will need to be replaced to keep you cool and to keep you feeling well. And, yes, there are medical conditions that require aggressive hydration, but that’s a whole other topic to say the least.

That said your body can withstand moderate exercise in all but the warmest climates for an hour or more without being topped up. You do have some “reservoir” capacity that’s built in. Human beings were roaming the earth pretty extensively before the invention of Gatorade. So to my fellow vacationers in northern Wisconsin, leave the water bottles behind when you climb up and down trails holding onto rocks and trees. You need both hands to keep yourself from falling. You won’t die of thirst. And the rest of us will be spared having to look at what you so inconsiderately left behind.